2B: Transport of materials across the plasma membrane

Question 1

• Allows some materials to pass.
  ->Water, oxygen, carbon dioxide
  – Prevents others from passing.
  ->Proteins, carbohydrates

Answer 1

Differentially (selectively permeable)

Question 2

Factors that determine how a substance may be transported across a plasma membrane:

Answer 2

• Size
  – Polar or Nonpolar
  – charge

Question 3

• governs biological systems
  – universe tends towards disorder (entropy)

Answer 3

2nd law of thermodynamics

Question 4

• Only small, relatively hydrophobicmolecules are able to
diffuse across a phospholipid bilayer at significant rates.

• Molecules have to dissolve in lipid interior

Answer 4

PASSIVE DIFFUSION

Question 5

Why is diffusion important to cells and humans?

Answer 5

• Cell respiration
• Alveoli of lungs
• Capillaries
• Red Blood Cells
• Medications: timerelease capsules

Question 6

Cell respiration

Answer 6

Proton motive force

Question 7

Alveoli of lungs

Answer 7

passive diffusion of gas exchange

Question 8

Medications: time release capsules

Answer 8

• cover takes a while to be digested (oral)
• can be injected to the bloodstream

Question 9

• Diffusion through protein channels which do not interact with hydrophobic interior

– For biological mol unable to dissolve in hydrophobic interior

– no energy needed

Answer 9

Facilitated diffusion

Question 10

With help

Answer 10

Facilitated

Question 11

Fast transport

Answer 11

open channel

Question 12

The passage of materials is aided by a concentration gradient and by a transport protein

Answer 12

Facilitated diffusion

Question 13

Two kinds of Proteins

Answer 13

Carrier Protein
Channel protein

Question 14

• bind specific molecules, undergo conformational change to release molecule
• ex. Glucose transporters

Answer 14

Carrier Proteins

Question 15

• form open pores for free diffusion
• found in gap junctions

Answer 15

Channel Proteins

Question 16

Molecules will randomly move through the _______ in Channel Proteins.

Answer 16

pores

Question 17

• Some Carrier proteins do not extend through the membrane.
• They _________ and _______ molecules through the lipid bilayer and release them on the opposite side.

Answer 17

bond and drag

Question 18

Other carrier proteins _________ to move materials across the cell membrane

Answer 18

change shape

Question 19

How do molecules move through the plasma membrane by facilitated diffusion?

Answer 19

Channel and Carrier proteins are specific:
• Channel Proteins allow ions, small solutes, and water to pass
• Carrier Proteins move glucose and amino acids
• Facilitated diffusion is rate limited, by the number of proteins channels/carriers present in the membrane.

Question 20

Most cells, including erythrocytes, are exposed to extracellular glucose concentrations that are higher than those inside the cell, so facilitated diffusion results in _________

Answer 20

the net inward transport of glucose

Question 21

• Water Channels
• Protein pores used during Osmosis

• provide corridors allowing water molecules to cross the membrane.
• Allow for fast transport
• water channel proteins make possible massive amounts of diffusion

Answer 21

Aquaporins

Question 22

– is the diffusion of water across a differentially permeable membrane.

Answer 22

OSMOSIS

Question 23

is the pressure that develops in a system due to osmosis.

Answer 23

Osmotic pressure

Question 24

determined by comparing total solute concentrations

Answer 24

Direction of osmosis

Question 25

more solute, less water

Answer 25

Hypertonic

Question 26

less solute, more water

Answer 26

Hypotonic

Question 27

equal solute, equal water

Answer 27

Isotonic

Question 28

depends on balancing water uptake and loss

Answer 28

Cell survival

Question 29

• Lysed (animal cell)
• turgid (Plant cell)
• Hypotonic solution

Answer 29

Freshwater

Question 30

• Normal (Animal cell)
• Flaccid (Plant cell)
• Isotonic solution

Answer 30

• Balanced

Question 31

• Shriveled (animal cell)
• plasmolyzed (plant cell)
• hypertonic solution

Answer 31

Saltwater

Question 32

Both solutions have the same osmolarity

Answer 32

volume unchanged

Question 33

Both solutions of water and sugar have identical osmolarity, but volume of the solution on the right is greater

Answer 33

Because only water is free to move

Question 34

– animal cell immersed in mild salt solution

• example:
blood cells in blood plasma
• problem: none
– no net movement of water
» flows across membrane equally, in both directions
– volume of cell is stable

Answer 34

Isotonic

Question 35

– a cell in fresh water

• example: Paramecium

• problem: gains water, swells & can burst
– water continually enters Paramecium cell

• solution: contractile vacuole
– pumps water out of cell
– ATP

plant cells
• turgid

Answer 35

Hypotonic

Question 36

Water regulation in paramecium

Answer 36

Contractile vacuole

Question 37

– a cell in salt water

• example: shellfish

• problem: lose water & die

• solution: take up water or pump out salt

plant cells
• plasmolysis

Answer 37

Hypertonic

Question 38

Plasmolysis

Answer 38

wilt

Question 39

Why is osmosis important to cells and
humans?

Answer 39

• Cells remove water produced by cell respiration.
• Large intestine cells transport water to bloodstream
• Kidney cells form urine

Question 40

Non-lipid soluble substances diffuse through

Answer 40

Membrane channels

Question 41

regulates the opening/closing of the channel.

Answer 41

membrane potential (voltage)

Question 42

permit the free passage of ions and small polar molecules through the outer membranes of bacteria.

Answer 42

Porins

Question 43

mediate the passage of ions across plasma membranes.

Answer 43

Ion channels

Question 44

open in response to the binding of neurotransmitters or other signaling molecules.

Answer 44

Ligand-gated channels

Question 45

open in response to changes in electric potential across the plasma membrane.

Answer 45

Voltage-gated channels